Generally, power control using Alternating Current AC power employs a zero-crossing control method and a phase control method. In the zero-crossing control method, when voltage is zero, that is, when AC power advancing while forming a sine wave advances by one cycle and reaches point A having zero voltage, as illustrated in FIG. 1A, On/Off control is performed. In order to supply 50% of supplied AC power, power is controlled in such a way as to repeat an On/Off operation every cycle in the zero-crossing control method.
Such a zero-crossing method is superior from the point of view of power noise.
However, the zero-crossing method requires a circuit for finding the zero point of AC power, that is, the point where voltage is zero after a cycle has completed, so that economical efficiency is low. Accordingly, the zero-crossing method can be utilized for expensive equipment, but has a disadvantage in that uniform power is not supplied in power control in which a control rate is low compared to the amount of AC power.
The phase control method controls power, which is supplied to a load, by varying the phase of supplied AC power as shown in FIG. 1B, so that the method is simple and, thus, may be used throughout all of industry. However, the phase control method has disadvantages in that noise is high and the method is not stable for power control for less than 50% of supplied AC power because switching on and off is performed at high voltage positions, and uniform power is not supplied.
That is, the conventional zero-crossing method and phase control method perform the On/Off control of power based on phase according to time, whereas a novel method proposed by the present invention performs the On/Off control of power based on the amount of voltage.